The disclosed technology relates generally to the formation of transferable micro devices. Semiconductor chip or die automated assembly equipment typically uses vacuum-operated placement heads, such as vacuum grippers or pick-and-place tools, to pick up and apply devices to a substrate. It is often difficult to pick up and place ultra-thin or small micro devices using this technology. Micro transfer printing permits the selection and application of these ultra-thin, fragile, or small micro devices without causing damage to the micro devices themselves.
Micro-structured stamps can be used to pick up micro devices from a native source substrate on which they are formed, transport the micro devices to a non-native destination substrate, and print the micro devices onto the destination substrate. Surface adhesion forces are used to control the selection and printing of these micro devices onto the destination substrate. This process can be performed massively in parallel, transferring hundreds to thousands of discrete structures in a single pick-up and print operation.
Electronically active components can be printed onto the non-native destination substrates. For example, these printing techniques can be used to form imaging devices such as flat-panel liquid crystal, LED, or OLED display devices or in digital radiographic plates. In each instance, the electronically active components are transferred from a native substrate to a destination substrate (e.g., a non-native substrate used to, for example, form an array of the active micro-device components). The active components are picked up from the native substrate and transferred to the destination substrate using an elastomer stamp.
Micro transfer printing enables parallel assembly of high-performance semiconductor micro devices onto virtually any substrate material, including glass, plastics, metals or other semiconductors. The substrates can be transparent or flexible, thereby permitting the production of flexible electronic devices. Flexible substrates can be integrated in a large number of configurations, including configurations not possible with brittle silicon-based electronic devices. Additionally, some plastic substrates, for example, are mechanically rugged and can be used to provide electronic devices that are less susceptible to damage or electronic performance degradation caused by mechanical stress. These materials can be used to fabricate electronic devices by continuous, high-speed, printing techniques capable of distributing electronic devices over large substrate areas at low cost (e.g., roll-to-roll manufacturing). Moreover, these conventional micro transfer-printing techniques can be used to print semiconductor devices at temperatures compatible with assembly on plastic polymer substrates. In addition, semiconductor materials can be printed onto large areas of substrates thereby enabling continuous, high-speed printing of complex integrated electrical circuits over large substrate areas. Moreover, fully flexible electronic devices with good electronic performance in flexed or deformed device orientations can be provided to enable a wide range of flexible electronic devices. However, conventional micro transfer printing techniques lack the reproducibility and precision required to efficiently produce electronics with high-density devices at low cost.
In a conventional micro transfer printing process, prior to transferring micro devices to a destination substrate, a native source substrate is provided with a sacrificial layer having sacrificial material and a plurality of micro devices formed at least in part over the sacrificial layer. The micro devices can be distributed over the native source substrate and spatially separated from each other by an anchor structure. The anchors are physically connected or secured to the native source substrate and tethers physically secure each micro device to one or more anchors.
Anchor structures that remain rigidly attached to the substrate and tether structures that join the releasable micro object to the anchor serve to maintain the spatial configuration of the micro objects upon partial or full separation of the micro object from the bulk substrate. When a transfer stamp picks up the device, the tethers for each device that is picked up are broken. Regarding micro transfer printing, see, for example, U.S. Pat. No. 7,982,296, issued Jul. 19, 2011, the content of which is incorporated herein by reference in its entirety.
However, it has been demonstrated that the release of the active micro-device components is not reliably controlled and not predictable, leading to inefficiencies, irreproducibilities, and errors. Therefore, there is a need for an improved method and system for efficiently and predictably controlling the release of semiconductor structures.